With the rapid growth in demand for mobile data fueled by the emergence of new consumer applications that require high quality of service, existing static mobile data pricing plans are no longer suitable. Although several dynamic pricing mechanisms have been proposed in the literature, they have not been widely adopted due to their associated implementation complexity, the lack of trust in the associated platforms, and the absence of automatic enforcement. To address these challenges, we propose a credible trust framework (CREDIT) that leverages well-established Ethereum smart contracts for service-level agreement (SLA) enforcement. CREDIT introduces a novel SLA verification mechanism through fair auditor selection and auditor payoff to ensure truthfulness, and hence reinforces trust between the various parties involved in CREDIT. A detailed game-theoretic analysis is provided to prove the credibility of CREDIT by using the principle of a strong Nash equilibrium. In addition, CREDIT is prototyped by leveraging the smart contracts of Ethereum Blockchain. The results achieved provide a valuable validation of the feasibility of CREDIT.